The degree of glycosylation of various proteins has been analyzed as an indicator that shows the condition of a living body. In particular, because the degree of glycosylation of hemoglobin (Hb), especially HbA1c, in blood cells reflects the history of glucose levels in a living body, it is regarded as an important indicator in the diagnosis and treatment of diabetes. HbA1c is HbA(α2β2) whose β-chain N-terminal valine has been glycosylated.
HbA1c has been analyzed by, for example, immunological methods, enzymatic methods, and high-performance liquid chromatography (HPLC) methods, among others. Although immunological methods and enzymatic methods are generally used in processing and analyzing large numbers of specimens, they are of low accuracy when determining the risk of complications. In contrast, although HPLC methods have poorer processing capabilities than immunological methods or enzymatic methods, they are useful in determining the risk of complications. However, due to the configuration of HPLC methods, the analysis apparatus is very large and costly.
On the other hand, electrophoresis chips are used generally in the analyses of biologically-relevant samples (see, for example, Patent Documents 1 and 2). Compared with HPLC methods, such electrophoresis chips allow the analyzers to be small.
A conventional electrophoresis chip has two capillary channels, one for sample introduction and the other for sample analysis. The two capillary channels intersect each other in a cross shape and are in communication with each other at the intersection. An analysis of a sample using such an electrophoresis chip is carried out as follows. First, a sample to be analyzed is introduced into a capillary channel for sample introduction. Then, a potential difference is created between both ends of the capillary channel for sample introduction to move the sample to the intersection. Next, a potential difference is created between both ends of a capillary channel for sample analysis to move the sample from the intersection into the capillary channel where the analysis of the sample is carried out.
Electrophoresis chips that have cross-shaped capillary channels that are in communication with each other at the intersection have problems as follows. Firstly, the configuration of such capillary channels is complex. Secondly, a voltage applying device for creating a potential difference between both ends of the two capillary channels needs to be provided separately. For these reasons, there are limitations in making such electrophoresis chips smaller and simpler. When the target of voltage application is changed from the capillary channel for sample introduction to the capillary channel for sample analysis, sample diffusion cannot be fully controlled if the voltage (potential difference) is not controlled properly. It may be possible in such a case that the amount of a sample introduced into the capillary channel for sample analysis is not uniform. Moreover, if the components of a sample have greatly different migration speeds, the composition of the sample at different portions within the capillary channel for sample introduction may be different from that of the original sample. As a result, the composition of a sample introduced into the capillary channel for sample analysis may not be uniform. Use of a long sample-plug for introduction into the capillary channel for sample analysis to prevent this phenomenon may result in a problem in that the ability to separate exerted in the capillary channel for sample analysis is impaired.
Patent Document 1: Japanese Patent No. 2790067
Patent Document 2: Japanese Patent No. 3656165